1. Field of the Invention
This invention generally relates to the field of materials construction and, more specifically, to an apparatus and method for constructing a corrugated composite stiffener.
2. Description of the Prior Art
Composite structures are desirable in many industries for many applications. For example, aircraft, space, and land/sea vehicles employ a variety of curved and multiple-contoured surface structures in their fabrication. Composite materials are commonly used for these structures because, among other desirable attributes, composite materials have high strength-to-weight ratios. Even so, composite structures formed from composite materials still need to be stiffened in some instances. Therefore, manufacturers of composite structures are continually searching for better and more economical ways of stiffening composite structures.
There are various systems and methods of stiffening composite structures. For example, in an aircraft context, hat and blade stiffeners are sometimes utilized. A blade stiffener is a thin element, often T-shaped in cross-section, that is affixed to a structure. The upper portion of the T-shape is affixed to the structure. The leg of the T-shape forms the blade and extends outward away from the structure, the stiffener extending along the length of the structure. The blade increases the moment of inertia of the entire cross-section to increase stiffness. Likewise, a hat stiffener has a three-dimensional cross-section that is typically symmetrical. The hat cross-section usually has a center portion from which two legs depend and terminate in feet. The hat stiffener may be attached to the structure at either the feet or the center portion. A problem with hat and blade stiffeners is that they can have special peel problems at their ends. Furthermore, when utilizing hat and blade stiffeners for strength in perpendicular directions, it becomes very expensive from a manufacturing standpoint because hat and blade stiffeners do not lend themselves well to criss-cross patterns.
Another common stiffening method is the use of honeycomb structures. However, honeycomb structures are usually manufactured as a sandwich structure, which means that they can trap moisture within them, leading to degradation, and are limited in depth because of volume and weight considerations. In addition, manufacturing honeycomb structures can be very expensive.
An additional method of stiffening composite structures is the use of corrugated stiffeners bonded to the structures. However, prior methods of constructing corrugated composite stiffeners are limited to hand layups, which are time consuming and produce stiffeners of uneven quality. Corrugated stiffeners of other materials, e.g., paper, may be created by feeding the material between toothed rollers, the teeth engaging and pressing the desired shape into the material. This method is not useful for resilient materials, such as prepreg composites.